GE Multilin L90 Line Current Differential System 5-2915 SETTINGS 5.7 CONTROL ELEMENTS5• LINE END OPEN PICKUP DELAY: This setting defines the pickup value for validation of the line end open conditionsas detected by the Line Pickup logic through the LINE PICKUP LEO PKP FlexLogic operand. The validated line end opencondition is a requirement for the POTT scheme to return a received echo signal (if the echo feature is enabled). Thisvalue should take into account the principle of operation and settings of the Line Pickup element.• POTT SEAL-IN DELAY: The output FlexLogic operand ( POTT OP ) is produced according to the POTT scheme logic. Aseal-in time delay is applied to this operand for coping with noisy communication channels. The POTT SEAL-IN DELAYdefines a minimum guaranteed duration of the POTT OP pulse. As this operand activates the trip table of the POTTscheme, the trip operands POTT TRIP A , B, C and 3P are sealed-in for the same period of time.• GND DIR O/C FWD: This setting defines the FlexLogic operand (if any) of a protection element that is used in additionto the Zone 2 for identifying faults on the protected line, and thus, for keying the communication channel and initiatingoperation of the scheme. Good directional integrity is the key requirement for an over-reaching forward-looking protec-tion element used as GND DIR O/C FWD. Even though any FlexLogic operand could be used as GND DIR O/C FWD allow-ing the user to combine responses of various protection elements, or to apply extra conditions through FlexLogicequations, this extra signal is primarily meant to be the output operand from either the negative-sequence directionalovercurrent or neutral directional overcurrent. Both of these elements have separate forward (FWD ) and reverse (REV )output operands. The forward indication should be used (NEG SEQ DIR OC1 FWD or NEUTRAL DIR OC1 FWD). For greatersecurity and to overcome spurious directional element operation during transients, adding at least 0.5 cycles of pickupdelay to the forward directional element is recommended.• POTT NO OF COMM BITS: This setting specifies the number of bits of the communications channel available for thescheme. The transmit codes and trip tables of the POTT scheme are the same as those for the permissive under-reaching transfer trip scheme. Please refer to the description of the PUTT scheme for more information.• POTT RX1 through POTT RX4: These settings allow the user to select the FlexLogic operands that represent thereceive signals for the scheme. Typically input contacts interfacing with a signaling system are used. In single-bit appli-cations, POTT RX1 must be used. In two-bit applications, POTT RX1 and POTT RX2 must be used. In four-bit applications,POTT RX1, POTT RX2, POTT RX3, and POTT RX4 must be used.
